Micro-transfer printing with selective component removal

ABSTRACT

An example of a method of micro-transfer printing comprises providing a micro-transfer printable component source wafer, providing a stamp comprising a body and spaced-apart posts, and providing a light source for controllably irradiating each of the posts with light through the body. Each of the posts is contacted to a component to adhere the component thereto. The stamp with the adhered components is removed from the component source wafer. The selected posts are irradiated through the body with the light to detach selected components adhered to selected posts from the selected posts, leaving non-selected components adhered to non-selected posts. In some embodiments, using the stamp, the selected components are adhered to a provided destination substrate. In some embodiments, the selected components are discarded. An example micro-transfer printing system comprises a stamp comprising a body and spaced-apart posts and a light source for selectively irradiating each of the posts with light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Pat. No. 9,358,775, entitledApparatus and Methods for Micro-Transfer Printing, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present specification generally relates to systems and methods formicro-transfer printing using a stamp and, in particular, to systems andmethods for controllably removing selected components adhered to stampposts from the stamp.

BACKGROUND

Conventional methods such as pick-and-place for applying integratedcircuits to a destination substrate are limited to relatively largedevices, for example having a dimension of a millimeter or more and itis often difficult to pick up and place ultra-thin, fragile, or smalldevices using such conventional technologies. More recently,micro-transfer printing methods have been developed that permit theselection and application of such ultra-thin, fragile, or small deviceswithout causing damage to the devices themselves.

Micro-transfer printing enables deterministically removing arrays ofmicro-scale, high-performance devices from a native source wafer,typically a semiconductor wafer on which the devices are constructed,and assembling and integrating the devices onto non-native destinationsubstrates, such as glass or polymer substrates. In a simple embodiment,micro-transfer printing is analogous to using a rubber stamp to transferliquid-based inks from an ink-pad onto paper. However, the “inks” aretypically composed of high-performance solid-state semiconductor devicesand the “paper” can be substrates, including glass, plastics, ceramics,metals, or other semiconductors, for example. An example micro-transferprinting process leverages engineered elastomer stamps coupled withhigh-precision motion-controlled print-heads to selectively pick up andprint large arrays of micro-scale devices from a source native waferonto non-native destination substrates.

Adhesion between an elastomer transfer device and a printable elementcan be selectively tuned by varying the speed of the print-head, forexample. This rate-dependent adhesion is a consequence of theviscoelastic nature of the elastomer used to construct the transferdevice. When the transfer device is moved quickly away from a bondedinterface, the adhesion is large enough to “pick” the printable elementsaway from their native substrates, and conversely, when the transferdevice is moved slowly away from a bonded interface the adhesion is lowenough to “let go” or “print” the element onto a foreign surface. Thisprocess may be performed as a massively parallel operation in which thestamps can transfer, for example, hundreds to thousands of discretestructures in a single pick-up and print operation.

Micro-structured stamps may be used to pick up micro devices from asource substrate, transport the micro devices to the destination, andprint the micro devices onto a destination substrate. A transfer device(e.g., micro-structured stamp) can be created using various materials.Posts on the transfer device can be designed to pick up material from apick-able object and then print the material to the target substrate.The posts can be formed in an array. For effective, high-yield printing,when picking up the material it is important that the stamp posts are inclose contact with the material (e.g., micro integrated circuits) beingtransferred or printed.

In any printing operation, it is important that the destination(receiving) substrate include functional devices at every desiredlocation on the destination substrate at the end of an assembly processand it is therefore important to provide methods and systems forensuring completely functional micro-transfer-printed structures.

SUMMARY

The present invention provides, inter alia, systems and methods fortransferring micro-devices from a native micro-device source wafer ormicro-device source substrate to a non-native destination substrate.According to some embodiments of the present invention, a method ofmicro-transfer printing comprises providing a component source wafer ormicro-device source substrate having micro-transfer printable componentsdisposed on or in the component source wafer or micro-device sourcesubstrate. Micro-transfer printable components and micro-transferprinted components can be referred to as components herein. Selectedones of the micro-transfer printable components are selected componentsand the micro-transfer printable components that are not selected arenon-selected components.

In some embodiments, a stamp comprising a body and spaced-apart postsprotruding away from the body to a distal end of the posts is provided.The posts have a spatial distribution on the body matched to a spatialdistribution of the micro-transfer printable components on or in thecomponent source wafer. The stamp can be a visco-elastic stamp, forexample comprising PDMS (polydimethylsiloxane). A provided light sourcecan controllably irradiate each of the posts with light through thebody.

Each of the posts is contacted to a component of the micro-transferprintable components to adhere the component to a distal end of thepost, for example with van der Waals forces. Posts contacting theselected components are selected posts and posts contacting thenon-selected components are non-selected posts. Controllably irradiatingwith a light source means that each of the posts can be irradiated, ornot, by the light source depending on whether the post is a selectedpost or a non-selected post. Selected posts can be irradiated andnon-selected posts can be non-irradiated.

The stamp with the adhered components is removed from the componentsource wafer and each of the selected posts are irradiated through thebody with the light to detach the selected components adhered to theselected posts from the selected posts, leaving the non-selectedcomponents adhered to the non-selected posts. The body and the posts aresubstantially transparent to the light.

Some embodiments of the present invention comprise providing adestination substrate and contacting the non-selected components to thedestination substrate using the stamp to adhere the non-selectedcomponents to the destination substrate, or to a layer on thedestination substrate, after detaching the selected components from theselected posts. The step of providing a destination substrate cancomprise providing an adhesive layer on the destination substrate andthe step of contacting the non-selected components to the destinationsubstrate can comprise directly contacting the non-selected componentsto the adhesive layer.

In some embodiments of the present invention, the component source wafercomprises a patterned sacrificial layer defining spaced-apartsacrificial portions and anchors, and the components are each disposedover a sacrificial portion and physically connected to an anchor by atether (e.g., at least one anchor by at least one tether). The steps ofcontacting the posts to the components and removing the stamp canfracture or break the tethers or separate the tethers from thecomponents.

Irradiation of selected posts can irradiate a distal end of the selectedposts, can irradiate selected components adhered to the distal ends ofthe selected posts, can irradiate a portion of the selected componentsadhered to the distal ends of the selected posts, can irradiate a layerof the selected components adhered to the distal ends of the selectedposts, or any combination of these. In some embodiments of the presentinvention, each of the components comprises an ablation layer and theirradiation of the selected posts vaporizes at least a portion of theablation layer of the selected components, for example a portion incontact with the distal end of the selected post.

In some embodiments, the posts and the components (e.g., a portionthereof) have different coefficients of thermal expansion (CTEs). Insome embodiments, irradiation of the selected posts can heat theselected posts or the distal ends of the selected posts so that thedistal end of the selected posts expands differently from the selectedcomponents adhered to the selected posts so that a thermal shear (ashear force due to temperature differences) takes place between theselected components and the distal ends of the selected posts, detachingthe selected components adhered to the distal ends of the selected postsfrom the distal ends of the selected posts. In some embodiments,irradiation of the selected components heats the selected components, aportion of the selected components, or a layer or portion of a layer ofthe selected components so that the distal end of the selected posts towhich the selected components are adhered expands differently from theselected components adhered to the selected posts so that a thermalshear takes place between the selected components and the distal ends ofthe selected posts, detaching (e.g., assisting in detaching along withstamp 10 motion) the selected components adhered to the distal ends ofthe selected posts from the distal ends of the selected posts.

In some embodiments of the present invention, each of the components istested before contacting the posts to the components to determine faultycomponents. Faulty components are selected so that each of the selectedcomponents is a faulty component. In some embodiments of the presentinvention, components are selected that are not faulty so that eachselected component is a non-faulty component. In some embodiments,selected components have at least one characteristic different from acharacteristic of non-selected components (e.g., independent of whetherany selected or non-selected component is faulty or not). In someembodiments, a mapping of the selected components and the non-selectedcomponents is provided.

In some embodiments of the present invention, a disposal area isprovided and the stamp is moved to the disposal area before the selectedposts are irradiated so that irradiating the selected posts detaches theselected components from the selected posts and disposes the selectedcomponents in the disposal area.

Some embodiments of the present invention comprise providing adestination substrate and moving the stamp to the destination substratebefore irradiating the selected posts so that irradiating the selectedposts detaches the selected components from the selected posts andadheres the selected components to the destination substrate or to alayer on the destination substrate. Non-selected components are notadhered to the destination substrate. In some embodiments, the selectedcomponents are in contact with the destination substrate during theirradiation. In some embodiments, the selected components in contactwith the destination substrate and the selected posts are removed fromthe selected components during the irradiation, so that the steps ofirradiation and removal of the stamp from the selected components occursat the same time, occur partially at the same time, or overlap in time.By removing the selected posts from the selected components during theirradiation step (e.g., by removing the stamp), the selected componentsare prevented from re-adhering to the selected posts after theirradiation is complete. In some embodiments, the selected componentsare adjacent to but not in contact with the destination substrate sothat the selected components are detached from the selected posts andthe selected components travel from the selected posts to thedestination substrate. In some embodiments where components compriseablation layers, the selected components can be forcibly ejected fromthe selected posts and propelled onto the destination substrate. Inembodiments relying on a shear force formed between the selected postsand the selected components, for example by heating and a CTE mismatchbetween the selected posts and the selected components, the selectedcomponents can fall from the selected posts to the destination substrateunder the force of gravity.

In some embodiments of the present invention, irradiating selected postscomprises irradiating a single post at a time. In some embodiments ofthe present invention, irradiating selected posts comprises irradiatingmultiple posts at a time. The light source can be a laser and methods ofthe present invention can comprise providing an optical system that cancontrollably direct a laser beam from the laser to one, or more thanone, selected post at a time.

In some embodiments of the present invention, each of the posts has adistal end protruding away from the body and the step of contacting eachpost to a component comprises contacting the distal end of the post tothe component to adhere the component to the distal end of the post.Irradiating the selected posts with the light source controllablyirradiates the distal end of each selected post or the selectedcomponent (e.g., portions of the selected component) to detach theselected component adhered to the selected post from the distal end ofthe selected post and from the selected post.

In some embodiments, selected components are first selected components,non-selected components are first non-selected components, and themethod comprises: providing a destination substrate; transferring thefirst selected components to first component locations; selecting secondselected components from among the first non-selected components,wherein the non-selected posts to which the second selected componentsare adhered are second selected posts; and transferring the secondselected components to second component locations by irradiating thesecond selected posts through the body with the light to detach thesecond selected components adhered to the second selected posts from thesecond selected posts. In some embodiments, the components define anarray, the first selected components are a first sparse subset of thearray, and the second selected components are a second sparse subset ofthe array.

In some embodiments of the present invention, a micro-transfer printingsystem comprises a stamp comprising a body and spaced-apart postsprotruding away from the body and a light source for controllablyirradiating each of the posts with light. The body and the posts aresubstantially transparent to the light. In some embodiments, a componentis adhered to each of the posts. In some embodiments, a component isadhered only to each of the non-selected posts. In some embodiments,each component comprises an ablation layer of ablative material that isin contact with the post to which the component is adhered. The ablationlayer can be a patterned layer or an unpatterned layer and can be orcomprise, for example, any one or more of a layer of metal, a layer ofdielectric material, a layer comprising a dye, a layer comprising ablack material, and a layer comprising carbon black.

In some embodiments of the present invention, the light emitted by thelight source is non-visible light and the ablation layer is at leastpartially transparent to visible light, for example 50% transparent.

In some embodiments of the present invention, the micro-transferprinting system comprises an optical system operable to controllablydirect light from the light source to the posts. Each of the posts cancomprise a distal end away from the body and the optical system can becontrollable to irradiate the distal end of one of the posts at a timeor to irradiate a distal end of each of multiple ones of the posts at atime.

In some embodiments of the present invention, the micro-transferprinting system comprises a motion-control system operable to move thestamp in at least two directions. The motion-control system can beoperable to controllably contact the posts to the components to adhereone of the components to each of the posts and remove the stamp from thecomponent source wafer with a component adhered to the distal end ofeach of the posts.

In some embodiments, a micro-transfer printing system comprises amotion-control system including a motion platform sized and shaped tohave a stamp attached or mounted thereto and a light source operable tocontrollably irradiate the posts with light when the stamp is attachedor mounted to the motion platform. The motion-control system is operableto move the stamp in at least two directions. In some embodiments, thestamp comprises a body and spaced-apart posts protruding away from thebody.

Certain embodiments of the present invention provide a system and methodfor micro-transfer printing multiple known-good die at one time from anative source wafer to a destination substrate. Certain embodiments ofthe present invention provide a system and a method for micro-transferprinting components having different characteristics using a singlepickup (e.g., and multiple prints).

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, features, and advantages ofthe present disclosure will become more apparent and better understoodby referring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a flow diagram illustrating methods in accordance with someembodiments of the present invention;

FIG. 2 is a schematic perspective of a component source wafer, stamp,motion, platform, and optical system illustrating some embodiments ofthe present invention;

FIG. 3 is a schematic cross section of a component source wafer with acomponent according to illustrative embodiments of the presentinvention;

FIG. 4 is a schematic cross section of component testing on a componentsource wafer according to illustrative embodiments of the presentinvention;

FIG. 5 is a schematic cross section of an array of selected andnon-selected components on a component source wafer according toillustrative embodiments of the present invention;

FIG. 6 is a schematic cross section of a stamp picking up componentsaccording to illustrative embodiments of the present invention;

FIG. 7A is a schematic cross section of a selected component removalfrom a stamp according to illustrative embodiments of the presentinvention;

FIG. 7B is a detail schematic cross section of a selected componentremoval from a stamp corresponding to FIG. 7A according to illustrativeembodiments of the present invention;

FIG. 8 is a schematic cross section of non-selected components printingto a destination substrate according to illustrative embodiments of thepresent invention;

FIG. 9 is a flow diagram illustrating methods in accordance with someembodiments of the present invention;

FIG. 10 is a schematic cross section of components printing to adestination substrate according to illustrative embodiments of thepresent invention;

FIG. 11 is a schematic cross section of selected component removal froma stamp according to illustrative embodiments of the present invention;

FIG. 12 is a schematic cross section of stamp removal of a non-selectedcomponent from a destination substrate removal according to illustrativeembodiments of the present invention;

FIG. 13 is a flow diagram illustrating a method in accordance with someembodiments of the present invention; and

FIGS. 14A-14C are schematic plan views of first and second locationsprinted to in successive printings on a destination substrate, accordingto illustrative embodiments of the present invention.

The features and advantages of the present disclosure will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar, orstructurally similar elements. The figures are not necessarily drawn toscale.

DETAILED DESCRIPTION

The present invention provides, inter alia, methods and systems forconstructing completely functional micro-transfer-printed systems. Suchcompletely functional systems can comprise one or more functionalcomponents on a destination substrate, for example a display substrate.Methods and systems in accordance with certain embodiments of thepresent invention enable micro-transfer printing known-good componentsfrom a component source wafer to a destination substrate. For example,known-good components can be transferred to a destination substrate bypicking up multiple components from the component source wafer with astamp, removing selected components (e.g., faulty components) from thestamp, and micro-transfer printing the remaining non-selected componentsto the destination substrate. For example, known-good components can betransferred to a destination substrate by picking up multiple componentsfrom the component source wafer with a stamp and micro-transfer printingonly selected (e.g., known-good) components to the destination substratewithout micro-transfer printing non-selected (e.g., faulty) components.Methods and systems in accordance with certain embodiments of thepresent invention enable micro-transfer printing components from acomponent source wafer to a destination substrate independently fromcomponents having at least one different characteristic. Methods andsystems in accordance with certain embodiments of the present inventionenable micro-transfer printing components from a stamp to a destinationsubstrate depending on the location of the components relative to thedestination substrate so that different subsets of components adhered tothe stamp are micro-transfer printed to different locations or areas ofthe destination substrate.

Referring to the flow diagram of FIG. 1, the schematic perspective ofFIG. 2, and the detail cross section of FIGS. 3-6, in some embodimentsof the present invention, a method of micro-transfer printing comprisesproviding in step 100 a component source wafer 20 comprising components22 disposed on or in component source wafer 20. Components 22 can bemicro-transfer printable components 22. In some embodiments, componentsource wafer 20 comprises a patterned sacrificial layer 66 definingspaced-apart sacrificial portions 68 and anchors 64 and each component22 is disposed over a sacrificial portion 68 and physically connected toan anchor 64 by a tether 62 (in some embodiments, a plurality of tethers62, optionally connected to a plurality of anchors 64). A stamp 10comprising a body 12 and spaced-apart posts 14 each protruding in adirection away from body 12 to a distal end 18 of post 14 is provided instep 110. Posts 14 can be in an array, for example evenly spaced in oneor two dimensions (e.g., with equal or unequal spacing in eachdimension). Distal end 18 of post 14 is the end of stamp post 14farthest away from stamp body 12. The positioning of stamp 10 relativeto component source wafer 20 can be controlled, for example, by amechanical motion-control system including motion platform 40 for movingstamp 10 in x, y, and, optionally, z dimensions (e.g., horizontally and,optionally, vertically). In some embodiments, an alternative oradditional motion platform for moving component source wafer 20 (e.g.,horizontally and, optionally, vertically) is provided. Posts 14 have aspatial distribution on body 12 matched to a spatial distribution ofcomponents 22 on component source wafer 20.

In step 120, an optical system 36 comprising an optics controller 38 andlight source 30 for controllably irradiating each post 14 with light 32through body 12 using optics 34 is provided and, in some embodiments,can be positioned relative to stamp 10 by mechanical motion platform 40.Provided light source 30 can controllably irradiate each post 14 withlight 32 through body 12. By controllably irradiating each post, it ismeant that each of the posts 14 can be irradiated by light 32, or not,depending on whether post 14 is a selected post 15 or a non-selectedpost 16. That is, when non-selected posts 16 are controllably irradiatedby light source 30, it is meant that non-selected posts 16 are notintentionally exposed to any light 32 from light source 30 (ignoring thepossibility that a small amount of stray light may be incident onnon-selected posts 16). In some embodiments, a light source 30 movesrelative to optics 34 to controllably irradiate different selected posts15. In some embodiments, one or more elements of optics 34 (e.g., one ormore mirrors) move relative to a light source 30 to controllablyirradiate different selected posts 15. In some embodiments, irradiationof each selected post 15 occurs automatically (e.g., due to automaticmotion of one or more elements, such as optics 34, light source 30,stamp 10, component source wafer 20, or destination substrate 70) upon astart input being received (e.g., into optics controller 38). Body 12and posts 14 can be substantially transparent to light 32 emitted bylight source 30. Optics controller 38 is shown disposed on optics 34 inFIG. 2, but optics controller 38 can be remotely located and operable toreceive and/or send signals, for example by one or more wires (e.g.,cables) or wirelessly.

Destination substrate 70 (e.g., as shown in FIG. 8) is provided in step130 and, in some embodiments, can be positioned relative to stamp 10 bymechanical motion platform 40. Thus, in some embodiments of the presentinvention, mechanical motion platform 40 can move destination substrate70 relative to stamp 10, can move stamp 10 relative to component sourcewafer 20, and can move light source 30 and optics 34 relative to stamp10, or any combination of these. In some embodiments, an alternative oradditional motion platform for moving destination substrate 70 (e.g.,horizontally and, optionally, vertically) is provided. In someembodiments of the present invention, motion platform 40 can be providedin a variety of forms. In some embodiments, motion platform 40 isprovided between at least a portion of optical system 36 (e.g., optics34) and stamp 10. In some embodiments, motion platform 40 is providedsuch that at least a portion of optical system 36 (e.g., optics 34) isdisposed between motion platform 40 and stamp 10. In some embodiments,motion platform 40 surrounds at least a portion of the perimeter ofstamp 10. Motion platform 40 can be integrated with stamp 10 or opticalsystem 36, for example.

Referring to FIG. 4, in step 140 each component 22 is tested, forexample with test fixture 90, to determine if component 22 is functional(step 141). In some embodiments, testing electrically stimulatescomponents 22 to respond with an electrical or optoelectrical responsethat is measured. In some embodiments, if a component 22 is notfunctional (i.e. component 22 is a faulty component) it is selected (aselected component 23) and if a component 22 is functional, it is notselected (a non-selected component 24), as shown in FIG. 5. (In someembodiments, if a component 22 is functional it is a selected component23 and if a component 22 is not-functional (i.e. component 22 is afaulty component), it is a non-selected component 24.) Results of thetest can be stored in memory 39 for example. (For illustration purposes,memory 39 is shown disposed on optics 34 in FIG. 2, but memory 39 can beremotely located and operable to receive and/or send signals, forexample by one or more wires (e.g., cables) or wirelessly.) Memory 39can be connected to optics controller 38 by one or more wires (e.g.,cables) or wirelessly. Memory 39 can be part of optical system 36. Instep 150 and as shown in FIG. 6, after removing sacrificial materialfrom sacrificial portions 68, stamp 10 is moved by motion platform 40 sothat distal end 18 of each post 14 is contacted to a component 22 (forboth selected components 23 and non-selected components 24) to adhere acomponent 22 to distal end 18 of each post 14. Stamp 10 with adheredcomponents 22 is then removed from component source wafer 20 in step155, breaking (e.g., fracturing) or separating tethers 62 to formseparated or broken tethers 63.

Referring to FIG. 7A and the detail of FIG. 7B, in response to testinformation stored in memory 39, optics controller 38 of optical system36 controls light source 30 to emit light 32 through body 12 with optics34 and irradiate each selected post 15 that contacts an adheredcorresponding selected component 23 to detach the corresponding adheredselected (e.g., faulty) component 23 from selected post 15, leavingnon-selected (e.g., known-good) components 24 adhered to correspondingnon-selected posts 16. It is noted that FIGS. 7A and 7B show an exampleoptical system 36 that has a different orientation of optics 34 andlight source 30 than the example shown in FIG. 2.

In some embodiments of the present invention, selected posts 15 of stamp10 can be irradiated to remove selected components 23 after moving stamp10 to a disposal area in a location remote from component source wafer20 and destination substrate 70 to avoid contamination of componentsource wafer 20 and destination substrate 70 with faulty selectedcomponents 23. In some embodiments, selected components 23 are lightlyadhered to a disposal substrate so that irradiated selected components23 adhere to the disposal substrate and non-selected components 24 thatare not irradiated do not adhere to the disposal substrate.

In some embodiments of the present invention, selected posts 15 of stamp10 can be irradiated while posts 14 are in contact with components 22while components 22 are on component source wafer 20, so that onlynon-selected components 24 are adhered to non-selected posts 16 whenstamp 10 is removed from component source wafer 20. In some embodiments,the steps of irradiation and removal of stamp 10 from selectedcomponents 23 occur at the same time, occur partially at the same time,or overlap in time. By removing stamp 10 (with non-selected components23 adhered to non-selected posts 16) from component source wafer 20during the irradiation, selected components 23 are prevented fromre-adhering to selected posts 15 after the irradiation is complete.

Referring to FIG. 8, in some embodiments non-selected components 24 onnon-selected posts 16 are contacted to destination substrate 70 toadhere non-selected components 24 to destination substrate 70 in step190 and stamp 10 is removed from destination substrate 70 in step 200with no components 22 adhered to stamp 10. Thus, only components 22 thatare tested and known to be good are transferred to destination substrate70. In some embodiments, selected components 23 are in contact withdestination substrate 70 during the irradiation process. In someembodiments, selected components 23 are not in contact with destinationsubstrate 70 during the irradiation process. For example, selectedcomponents 23 can be within 20 μm (e.g., within 10 μm, within 5 μm,within 2 μm, or within 1 μm) of destination substrate 70, but not incontact, during irradiation. Destination substrate 70 is shown coatedwith optional adhesive layer 72 such that non-selected components 24directly contact adhesive layer 72. In some embodiments, no suchadhesive layer is present (e.g., such that non-selected components 24are directly printed onto destination substrate 70).

In some embodiments, after known-good components 22 are micro-transferprinted to destination substrate 70, any components 22 determined to bemissing (step 220) can be printed by repeating the printing processuntil no components 22 are missing and the process is done (step 230).For example, one or more missing components 22 can be printed by onlypicking up and testing a single component 22 at a time and printing thesingle component 22 (e.g., if it is a functional component 22).

In some embodiments, ablation occurs during irradiation that leads tocomponent 22 separation. Selected components 23 can be forcibly ejectedfrom selected posts 15 due to ablation (e.g., of an ablation layer 50 ofselected components 23 disposed in contact with selection posts 15). Insome embodiments, selected components 23 are detached from selectedposts 15 by a shear force that forms between selected posts 15 andselected components 23 when the selected posts 15 and selectedcomponents 23 have a CTE mismatch and are, for example, heated (e.g., byirradiation). Non-selected components 24 on non-selected posts 16 arenot detached from the non-selected posts (e.g., because no differentialthermal expansion occurs between the non-selected posts 16 andnon-selected components 24) and are not adhered to the substrate whenstamp 10 is removed from the substrate. A CTE mismatch can occur with orwithout the presence of an ablation layer 50 in components 22.

Optionally, after selected posts 15 are irradiated to detach selectedcomponents 23, selected posts 15 can be examined in step 170 to verifythat selected components 23 are indeed detached (step 180). Such adetermination can be made using an optical camera and one or more imagerecognition techniques, for example. If any selected components 23 arestill attached to selected posts 15, irradiation step 160 can berepeated for selected posts 15 with attached selected components 23 (orall selected posts 15). In step 150, missing components 22 aredetermined and additional components 22 from a component source wafer 20that are tested and known to be good can be printed to locations ondestination substrate 70 that were not printed with non-selectedcomponents 24 in step 190.

The method illustrated in FIG. 1 comprises removing selected (faulty)components 23 from stamp 10 before printing non-selected (known-good)components 24 to destination substrate 70. In some embodiments of thepresent invention, selected (known-good) components 23 in contact withdestination substrate 70 can be removed from stamp 10 and non-selected(faulty) components 24 removed with stamp 10 from destination substrate70. In such embodiments, if a component 22 is functional it is selected(a selected, known-good component 23); if a component 22 is notfunctional, it is not selected (a non-selected faulty component 24).This selection criterion is the inverse of the selection criterion forthe illustrative embodiment in FIG. 1.

Referring to FIG. 9, in some embodiments of the present invention, steps100-150 are performed as described above. However, rather than removingselected (non-functional) components 23 from selected posts 15 of stamp10, for example as in step 160 of FIG. 1, all components 22 adhered toposts 14 of stamp 10 are contacted or located closely adjacent to orabove destination substrate 70, as shown in step 191 and FIG. 10. Instep 160 and as shown in FIG. 11, distal ends 18 of selected posts 15 incontact with selected (functional) components 23 are irradiated todetach selected components 23 from distal ends 18 of selected posts 15.Stamp 10 is then removed from destination substrate 70 with non-selected(non-functional) components 24 in contact with non-selected posts 16 instep 201 and as shown in FIG. 12. The irradiation and removal steps 160,201 can be executed simultaneously or overlap in time to facilitatedetachment of selected (known-good) components 23 and removal ofnon-selected (faulty) components 24. In some embodiments, afterknown-good components 22 are micro-transfer printed to destinationsubstrate 70, any components 22 missing from destination substrate 70can be determined in step 220 and printed by repeating the printingprocess including step 150. For example, one or more missing components22 can be printed by only picking up and testing a single component 22at a time and printing the single component 22 (e.g., if it is afunctional component 22).

In some embodiments, selected components 23 are in contact withdestination substrate 70 during the irradiation process. In someembodiments, selected components 23 in contact with destinationsubstrate 70 and selected components 23 are removed from selected posts15 during irradiation, so that the steps of irradiation and removal ofstamp 10 from selected components 23 occur at the same time, occurpartially at the same time, or overlap in time. By removing selectedposts 15 (with the stamp 10) from selected components 23 during theirradiation, selected components 23 are prevented from re-adhering toselected posts 15 after the irradiation is complete. In someembodiments, selected components 23 are adjacent to but not in contactwith destination substrate 70 so that selected components 23 aredetached from selected posts 15 and selected components 23 travel (e.g.,drop) from selected posts 15 to destination substrate 70. For example,selected components 23 can be within 20 μm (e.g., within 10 μm, within 5μm, within 2 μm, or within 1 μm) of destination substrate 70, but not incontact, when detached.

In some embodiments, an ablation layer 50 is ablated to detach selectedcomponents 23 from selected posts 15. Selected components 23 can beforcibly ejected from selected posts 15 and propelled onto destinationsubstrate 70. In some such embodiments, a gap between selectedcomponents 23 and destination substrate 70 can enable the transfer ofselected components 23 to destination substrate 70 without re-adhesionof selected components 23 to selected posts 15. Re-adhesion can resultin a failed transfer. In some embodiments, shear force formed betweenselected posts 15 and selected components 23, for example by heating anda CTE mismatch between selected posts 15 and selected components 23,causes detachment of selected components 23 from selected posts 15.Selected components 23 can contact destination substrate 70 to enableadhesion of selected components 23 to destination substrate 70,promoting transfer. A CTE mismatch can occur with or without thepresence of an ablation layer 50 in components 22.

Stamp 10 can then be cleaned in step 210. As an example, stamp 10 can becleaned by contacting non-selected components 24 to an adhesive cleaningsurface in a disposal area (e.g., a sticky tape). As an example, stamp10 can be cleaned by irradiating distal ends 18 of non-selected posts 16in a suitable disposal location to remove non-selected components 24from non-selected posts 16. In some embodiments, after known-goodcomponents 22 are micro-transfer printed to destination substrate 70,any components 22 determined to be missing (step 220) can be determinedin step 150 and printed by repeating the printing process until nocomponents 22 are missing and the process is done (step 230). Forexample, one or more missing components 22 can be printed by onlypicking up and testing a single component 22 at a time and printing thesingle component 22 (e.g., if it is a functional component 22).

According to some embodiments of the present invention, and as shown inFIG. 7A, a micro-transfer printing system 99 comprises a stamp 10 thatcomprises a body 12 and spaced-apart posts 14 protruding away from body12. A light source 30 can controllably (e.g., selectively) irradiateeach selected post 15 with light 32. (Light 32 can generally be anyelectromagnetic radiation, such as, for example, visible light,ultraviolet light, or infrared light.) In some embodiments, a component22 (either a selected component 23 or a non-selected component 24) isadhered to each post 14. Body 12 and posts 14 are substantiallytransparent to light 32 emitted by light source 30. By substantiallytransparent it is meant that light 32 from light source 30 can passthrough body 12 and posts 14 with sufficient luminance to detachcomponents 22 from distal end 18 of selected posts 15. As a non-limitingexample, a body 12 and posts 14 that are substantially transparent tolight 32 from a light source 30 can be at least 70% (e.g., at least 80%or at least 90%) transparent. Posts 14 and body 12 can be made from asame material or comprise different materials. Irradiation of selectedposts 15 can irradiate a distal end 18 of selected posts 15, canirradiate selected components 23 adhered to distal ends 18 of selectedposts 15, can irradiate a portion of selected components 23 adhered todistal ends 18 of selected posts 15, can irradiate a layer of selectedcomponents 23 adhered to distal ends 18 of selected posts 15, or anycombination of these. Irradiating a selected post 15 with an adheredselected component 23 detaches (e.g., causes detachment of) the selectedcomponent 23 from the distal end 18 of the selected post 15.

In some embodiments, components 22 comprise an ablation layer 50 ofablative material 52 in contact with each post 14 to which a component22 is adhered (e.g., adhered to distal end 18 of selected post 15).Ablative material 52 is chosen to absorb light 32 emitted from lightsource 30, for example to selectively absorb light 32 from light source30, and, in some embodiments, decomposes (e.g., vaporizes) in responseto the absorption. Ablative material 52 can be at least partiallytransparent to visible light and light 32 emitted from light source 30can be invisible, for example infra-red or ultra-violet. Thus, in someembodiments, light 32 emitted by light source 30 is non-visible lightand ablation layer 50 is at least partially transparent to visiblelight, for example at least 30% (e.g., at least 40%, at least 50%, atleast 70%, at least 80%, or at least 90%) transparent to visible light.Ablation of ablation layers 50 detaches (e.g., assists in detachingalong with stamp 10 motion) selected components 22 from posts 15.

In some embodiments, stamp 10 is a visco-elastic stamp 10, for example aPDMS (polydimethylsiloxane) stamp 10. Body 12 and posts 14 can be madefrom a same material (e.g., PDMS) and have different mechanicalproperties (e.g., due to a different composition of the material in thebody 12 and posts 14). In some embodiments, light source 30 is a laser.In some embodiments, an optical system 36 (e.g., comprising optics 34,light source 30, and optics controller 38) controllably directs light 32from light source 30 to one or more posts 14, e.g., selected posts 15.In some embodiments, optical system 36 (light source 30, opticscontroller 38, and optics 34) is controllable to irradiate a distal end18 of one selected post 15 at a time (e.g., using one or more waveguides, lenses, or mirrors). In some embodiments, light source 30 oroptics 34 move, and subsequently light source 30 emits light 32, duringcontrolled irradiation such that each emission of light 32 irradiatesonly one selected post 15 due to alignment between light source 30,optics 34, and one selected post 15. In some embodiments, optical system36 is controllable to irradiate distal ends 18 of multiple selectedposts 15 at a time (e.g., using one or more wave guides, lenses, beamsplitters, or mirrors). In some embodiments, light source 30 or optics34 move, and subsequently light source 30 emits light 32, duringcontrolled irradiation such that each emission of light 32 irradiatesmultiple selected posts 15 due to alignment between light source 30,optics 34, and multiple selected posts 15 (e.g., where multiple selectedposts 15 are only a portion or all of selected posts 15).

In some embodiments, micro-transfer printing system 99 comprises memory39. In some embodiments, memory 39 can store a mapping of selectedcomponents 23 and non-selected components 24. A mapping can correspondto locations of selected components 23 and non-selected components 24 oncomponent source wafer 20, for example. In some embodiments, a mappingof selected components 23 and non-selected components 24 is formed ordetermined based, at least in part, on input from test fixture 90. Insome embodiments, a mapping of selected components 23 and non-selectedcomponents 24 is formed or determined based, at least in part, on knownlocations of a first set of components 22 and a second set of components22, the sets disposed on or in a component source wafer 20 and thesecond set having at least one characteristic different from the firstset. In some embodiments, a mapping of selected components 23 andnon-selected components 24 is formed or determined based, at least inpart, on known locations of a first set of components 22 and a secondset of components 22 on a destination substrate 70 after their printing.A mapping can be used by optics controller 38 for controllablyirradiating selected posts 15. Irradiating selected posts 15 can occurautomatically (e.g., by automatic and controlled movement of optics 34and/or light source 30 relative to stamp 10), for example, when using amapping.

In some embodiments, micro-transfer printing system 99 comprises amotion-control system (e.g., including motion platform 40) for movingstamp 10 (e.g., relative to component source wafer 20) and, optionally,relative to at least some portions of optical system 36. In someembodiments, a motion-control system can move stamp 10 between alocation corresponding to component source wafer 20 (e.g., overcomponent source wafer 20) and a location corresponding to destinationsubstrate 70 (e.g., over destination substrate 20) and, optionally,vertically, for example when in the location corresponding to thecomponent source wafer 20 or the destination substrate 70. In someembodiments, a motion-control system can also move stamp 10 to adisposal area (e.g., with a disposal substrate in the disposal area). Insome embodiments, stamp 10 is mounted or attached to a motion-controlsystem (e.g., a motion platform 40 of the motion-control system). Stamp10 can be mounted or attached to a motion-control system by, forexample, one or more clamps, one or more fasteners, one or more braces,or adhesive. In some embodiments, micro-transfer printing system 99comprises a component source wafer 20 comprising micro-transferprintable components 22. A motion-control system can be adapted tocontrollably contact posts 14 to components 22 to adhere a component 22to each post 14 and remove stamp 10 from component source wafer 20 witheach component 22 adhered to a distal end 18 of a post 14.

In some embodiments, each post 14 comprises a distal end 18 thatprotrudes away from body 12, components 22 are adhered to distal end 18of selected posts 15, and light source 30 controllably irradiates distalend 18 of each selected post 15.

Component source wafer 20 can be any wafer suitable for the assembly orconstruction of components 22 on patterned sacrificial portions 68, forexample glass, mono-crystalline semiconductor (e.g., silicon) orcompound semiconductor (e.g., GaN or GaAs), quartz, sapphire, orceramic. Component source wafers 20 can have a diameter, for example,greater than or equal to 10 cm (e.g., greater than or equal to 15 cm, 20cm, 25 cm, 30 cm, 40 cm, or 100 cm). In some embodiments, a componentsource wafer 20 has a diameter that is less than or equal to 200 cm.Suitable component source wafers 20 are found in the semiconductor,integrated circuit, and display industries and can be processed, forexample, using photolithographic methods and materials. Patternedsacrificial layer 66 can be a patterned oxide or nitride layer (such assilicon oxide or silicon nitride) that is differentially etchable fromthe remainder of component source wafer 20 or can be a layer comprisingdesignated portions in a layer of component source wafer 20 (e.g.,etchable portions under components 22). In some embodiments, componentsource wafer 20 comprises an anisotropically etchable crystallinematerial (such as silicon) that can be anisotropically etched to removematerial from sacrificial portions 68 to release components 22 fromcomponent source wafer 20, leaving components 22 each attached by one ormore tethers 62 to one or more anchors 64.

Referring back to FIG. 3, components 22 can be any of a wide variety ofdevices, such as, for example but not limited to, electronic, optical,optoelectronic, mechanical, or piezoelectric devices. Components 22 canbe optically emissive or responsive and can be light emitters (such asLEDs), light sensors (such as photodiodes), lasers, or electricaljumpers. Components 22 can be integrated circuits (for example CMOS,bipolar, or mixed circuits) and comprise electronically active orpassive elements or both. Components 22 can be constructed usingphotolithographic methods and materials. Components 22 can have, forexample, at least one of a width, length, and height from 2 μm to 1000μm (for example 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, 20 to 50 μm, 50 μmto 100 μm, 100 μm to 250 μm, 250 μm to 500 μm, or 500 μm to 1000 μm).Components 22, for example, can have a doped or undoped semiconductorstructure 82 substrate thickness from 2 μm to 50 μm (for example from 2to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm). Components 22 canhave a length greater than width, for example having an aspect ratiogreater than or equal to 2 (for example greater than or equal to 4, 8,10, 20, or 50). Components 22 can comprise component contact pads 83that are adjacent to the ends of components 22 along the length ofcomponents 22 to provide electrical contact to components 22. Components22 can comprise a patterned dielectric layer 87 to provide electricalinsulation and electrodes 84 to provide electrical connection tocomponent contact pads 83. An encapsulation layer 88 (for example asecond dielectric layer of silicon dioxide or nitride) can protectcomponents 22 and, optionally, provide a tether 62. An optional ablationlayer 50 of ablative material 52 can be provided, for example usingphotolithographic process and materials, on a surface of components 22that is contacted by distal end 18 of posts 14.

In some embodiments, subsets of components 22 disposed on or incomponent source wafer 20 have one or more different characteristicsthat are not merely natural variation within manufacturing tolerances ofcomponents 22. A characteristic that is different between two components22 can be, for example, size, shape, an optical property, an electronicproperty (e.g., piezoelectricity), or a mechanical property. Forexample, a different characteristic can be emission wavelength (e.g., ifcomponents 22 are light emitters), circuit design (e.g., if components22 are controllers, such as micro-controllers), or properties that aresensed or sensitivity to those properties (e.g., if components 22 aresensors). If components 22 disposed on or in component source wafer 20are light emitters, a characteristic that is different can be, forexample, color (e.g., emission wavelength), hue, tint, shade,brightness, efficiency, or angular distribution of emitted light.Selected ones of components 22 can be selected based on a characteristicthat they have, with non-selected ones of components 22 having at leastone different characteristic. In some embodiments, non-selectedcomponents 24 having a different characteristic are micro-transferprinted in a later step (e.g., after moving a position of stamp 10having non-selected components 24 still disposed thereon relative todestination substrate 70). In some embodiments, selected components 23are not uniform, for example selected components 23 can comprisecomponents 22 having different characteristics. For example, selectedcomponents 23 can include two or more colors of light-emitting diodes.

A first set of components 22 disposed on or in component source wafer 20can be interspersed with (or adjacent to) a second set of components 22disposed on or in component source wafer 20 that has at least onedifferent characteristic. In some embodiments, component source wafer 20is fabricated having a known distribution of a first set of components22 and a second set of components 22, the first set of components 22having at least one characteristic different from a characteristic ofthe second set of components 22. Selected components 23 can be orcomprise either the first set or the second set (with non-selectedcomponents 24 being or comprising the other set) (e.g., independent ofwhether selected components 23 and/or non-selected components 24comprises one or more faulty components 22). A mapping can be formed ordetermined based on the known distributions of the first set and thesecond set and, for example, input into memory 39 in order tomicro-transfer print the first set or the second set independent of theother set (e.g., using steps described above). Components 22 havingdifferent characteristics can be fabricated on a single component sourcewafer 20 (as opposed to multiple component source wafers 20) in order tomore efficiently utilize valuable material and/or reduce manufacturingsteps, thereby reducing costs. For example, different colorlight-emitting-diodes can be fabricated on a single component sourcewafer 20 or different integrated circuits can be fabricated on a singlecomponent source wafer 20.

In some embodiments, subsets of components 22 adhered to stamp 10 arerepeatedly selected and transferred to destination substrate 70. Forexample, referring to flow diagram FIG. 13, an array of components 22can be picked up by stamp 10 in step 150 and moved by motion platform 40to a location with respect to destination substrate 70 in step 205, forexample components 22 adhered to stamp 10 are contacted or locatedclosely adjacent to and above destination substrate 70. Selectedcomponents 23 representing a subset of components 22 adhered to stamp10, for example a sparse array of components 22, are selected in step195 and transferred to first locations 74 on destination substrate 70 byirradiation in step 160, for example as described above. (The selectionstep 195 can be done at any convenient time, for example, but notlimited to, before stamp 10 is moved.) If all of components 22 aretransferred and none remain adhered to stamp 10, the process iscompleted and can be repeated by picking up a new set of components 22from component source wafer 10 in step 150. If some components 22 remainadhered to stamp 10 (e.g., some of the components were non-selectedcomponents 24 during the first printing), the process is repeated bymoving stamp 10 to a new location (such that a second subset ofcomponents 22 are in second locations 76) over destination substrate 70(step 205), a different subset of components 22 adhered to stamp 10 isselected (step 195) and transferred to destination substrate 70 (step160). Subsets of components 22 disposed on stamp 10 (and selected asselected components 23 in successive printing operations) can beinterspersed or separated (e.g., adjacent). Second locations 76 ondestination substrate 70 can be adjacent, disjointed, or overlapping tofirst locations 74 in which a first subset of components 22 have alreadybeen printed, as shown, for example, in FIG. 14A, FIG. 14B, and FIG.14C, respectively. For example, a first subset of components 22 in afirst locations 76 can be interspersed with a second subset ofcomponents 22 disposed in a second locations 76. A distance betweensecond locations 76 and first locations 74 can be less than acharacteristic separation of a first subset of components 22 that havebeen disposed in first locations 74.

Thus, components 22 can be distributed in a variety of arrangements ondestination substrate 70 different from the arrangement of components 22on stamp 10 with multiple printing steps and without having to pick upadditional components 22 from component source wafer 20, therebyimproving the printing throughput and print location flexibility. Forexample, a 4×4 array of components 22 can be picked up by stamp 10 fromcomponent source wafer 10, a first 2×2 subset of the 4×4 array isselected and transferred to first locations 74 on destination substrate70, then a second 2×2 subset of the remaining twelve components 22 inthe 4×4 array is selected and transferred to second locations 76 ondestination substrate 70, then a third 2×2 subset of the remaining eightcomponents in the 4×4 array is selected and transferred to thirdlocations on destination substrate 70, and then the remaining fourcomponents in the 4×4 array are selected and transferred to fourthlocations on destination substrate 70. If the 2×2 arrays comprise, forexample, every other component 22 of the 4×4 array of components 22 inone or two dimensions, then the 2×2 arrays are sparse and the printedarea of destination substrate 70 can be larger than the area of the 4×4array, resulting in geometric magnification of the 4×4 printed area ondestination substrate 70 with respect to the area of component sourcewafer 10 from which the 4×4 array of components 22 was picked up. Insome embodiments, the arrangement or number of selected components 23transferred to destination substrate 70 is different in differenttransfer steps. By performing a single component pick up from thecomponent source wafer 20 and four printing steps, throughput isimproved.

Test fixture 90 can be an electronic, mechanical, optical, orcombination fixture. Generally, test fixture 90 can include anycombination of elements that senses a response from components 22. Insome embodiments, test fixture 90 provides power to components 22 fortesting purposes. Test fixture 90 can be constructed and arranged totest only one component 22 or a plurality of components 22 at a time.For example, test fixture 90 can be a bed-of-nails electronic probe withcircuits for providing electrical power to components 22 throughelectrodes 84 and component contact pads 83 and electronic or opticalsensing circuits for sensing and measuring a response of components 22.In some embodiments, component source wafer 20 comprises wires(electrical conductors) electrically connected to components 22 throughelectrodes 84 and component contact pads 83 and controlled by testfixture 90, for example as shown in FIG. 4. The wires can be routed overor under tethers 62 or form a portion of tethers 62 and/or formed overexposed portions of sacrificial portions 68 and subsequently removed(e.g., by unpatterned or patterned etching) before pickup by stamp 10.Examples of such wires are shown in FIGS. 3 and 4, where wires 83connected to contact pads 83 are exposed on a portion of sacrificialportion 68 and extending past anchor 64, thereby allowing for a closedcircuit to be formed for testing. Additional examples of such wires aredescribed in U.S. Pat. Nos. 9,923,133 and 9,142,468, both entitledStructures and methods for testing printable integrated circuits. Testfixture 90 can comprise a computer for controlling components 22 andmeasuring, analyzing, reporting, and storing test information andresults in memory 39. Testing with test fixture 90 can be done eitherbefore, or after, sacrificial material in sacrificial portion 68 isremoved, e.g., by etching.

Motion platform 40 can be a computer-controlled electro-mechatronicassembly, for example comprising stepper motors for providing multi-axismovement of the platform. Motion platform 40 can comprise a transparentstructure (for example a glass or transparent polymer plate) in afixture for holding stamp 10 and allowing light 32 to pass through thetransparent structure to enter stamp 10. Suitable motion platforms 40are commercially available or can be adapted for use in a micro-transferprinting system 99.

Light source 30 can be a laser that emits laser light 32 (e.g., intooptics 34). Optics 34 can comprise, for example, one or more of one ormore mirrors, one or more refractive lenses, one or more diffractors,one or more acousto-optic modulators (AOMs), one or more electro-opticmodulators (EOMs), one or more beam splitters, and one or more rotatingpolygonal mirrors to control emitted light 32. For example, light 32from light source 30 can be scanned over the back surface of stamp 10and posts 14 and temporally controlled to irradiate any particularselected post 15 (or group of selected posts 15), or not by a real-timeelectronic/computer controller. Optics controller 38 can receiveinformation from test fixture 90 to specify selected components 23 andselected posts 15. For example, a mapping of selected component 23locations and non-selected component 24 locations can be formed based,at least in part, on input from test fixture 90, and used by opticscontroller 38 for controllably irradiating selected posts 15. Suitableor adaptable examples of optical systems 36 and light-control methodsand devices are known in the art. In some embodiments, at least someelements of optical system 36 can be moved by motion platform 40relative to stamp 10 to align light 32 emitted by light source 30 withselected posts 15 and selected components 23. In some such embodiments,light 32 is mechanically scanned over the selected posts 15. Hence, insome embodiments, single selected posts 15 are irradiated at a time tosequentially detach selected components 23. In some embodiments, morethan one selected post 15 is irradiated at a time, for example usingoptics 34 to divide a laser beam (e.g., light 32) into multiple beams.In some embodiments, light source 30 is constructed and disposed suchthat no optics are needed to controllably irradiate each of the posts 14in stamp 10. For example, if light source 30 is disposed over stamp 10and has a small beam width, light source 30 alone can be sufficient toprovide controllable irradiation of posts 14 (e.g., by movement of stamp10 or light source 30).

Stamps 10 having protruding posts 14 used for micro-transfer printingthat can be used in systems and methods described herein are describedin U.S. Pat. No. 9,412,727 entitled Printing transferable componentsusing microstructured elastomeric surfaces with pressure modulatedreversible adhesion. Such stamps 10 can comprise PDMS(polydimethylsiloxane with or without an additive, such as Dow Sylgard184 Elastomer Base and Curing Agent by Dow Corning Corporation ofAuburn, Mich.). Stamp 10 can be made by providing aphotolithographically defined mold structure that holds a support inalignment with a stamp mold. The stamp mold can provide a body cavityand one or more structured cavities (e.g., defining posts 14). A liquidcurable material is injected into the mold cavity and the assembly issubjected to heat to cure the liquid curable material to form the layercorresponding to the mold. The mold is removed from the mold structureand the stamp 10 removed from the mold.

Stamp body 12 can have a range of thicknesses from 0.50 μm to 1000 μm(e.g., 200 μm). Stamp posts 14 can have a length ranging from 5 μm to100 μm (e.g., 20 μm), and a height-to-width ratio of 1:4 to 4:1 (or, insome embodiments, more than 4:1). Posts 14, for example, can have a sizethat is larger or smaller than, or matched to, the size or area ofcomponents 22. Additionally, posts 14 can have a shape (incross-section) that is different than the shape of a contact surface ofcomponents 22 or a shape that corresponds to a shape of a contactsurface of components 22. Stamp 10 can be provided on a support (notshown in the Figures for simplicity), for example glass, soda-limeglass, borosilicate glass, Pyrex, metal, ceramic, polymer, or asemiconductor (e.g., a wafer or portion of a wafer). The support canhave a thickness ranging from 0.5 mm to 10 mm. These ranges and valuesare illustrative and not limiting and other materials and sizes areincluded in certain embodiments. Systems comprising motion platforms 40for micro-transfer printing components 22 from a component source wafer20 to a destination substrate 70 have been constructed and used to makea wide variety of applications, including, for example active-matrixcolor displays with pixel controllers and inorganic LEDs.

Components 22 can be at least partially coated with an ablative material52 in an ablation layer 50. Ablative material 52 can absorb light 32emitted from light source 30 and, in some embodiments, vaporizes (e.g.,generates a plasma) that provides pressure pushing components 22 awayfrom distal end 18 of selected posts 15 to detach (e.g., assist indetaching along with stamp 10 motion) components 22 from selected posts15 (step 160). Not all of the ablative material 52 is necessarilyremoved when irradiated by light 32. Ablation layer 50 can be apatterned layer or an unpatterned layer and can be a layer of metal, alayer of dielectric material, a layer comprising a dye, a layercomprising a black material, or a layer comprising carbon black. In someembodiments, ablative material 52 is a dielectric, polymer, or resin andcan comprise a dye or other light-absorbing material such as carbonblack. Ablative material 52 can be coated, for example, spin coated,spray coated, or hopper coated, and, in some embodiments, patternedusing photolithographic patterning methods. Ablative material 52 can bea photoresist material. The light-absorbing material can be matched tolight 32 so that the light-absorbing material selectively andefficiently absorbs a frequency of light 32 emitted from light source30. The frequency of light 32 emitted from light source 30 can generallybe any electromagnetic radiation, such as, for example, visible light,ultra-violet light, or infra-red light. In some embodiments, ablativematerial 52 is substantially transparent to visible light, so thatvisible light emitted from component 22 can pass through ablation layer50. In some embodiments, ablative material 52 absorbs visible light. Insome embodiments, ablative material 52 is a metal, for example, gold,silver, or aluminum metal and can be part of a patterned circuit on asurface of components 22.

In some embodiments of the present invention, light 32 that irradiatesselected posts 15 can irradiate distal ends 18 of selected posts 15 orcan irradiate components 22 (e.g., portions of components 22 or one ormore layers of or on components 22) or any combination of such elements.Light 32 absorbed by any one or both of the distal ends 18 of selectedposts 15 and components 22, can heat one or both of the distal ends 18of selected posts 15 and components 22. If the CTEs of various materialsare different, when the materials are heated a shear force will bepresent between the materials with different CTEs as the differentmaterials expand by different amounts. This shear force, if presentbetween distal ends 18 of selected posts 15 and selected components 23(e.g., portions of selected components 23) can cause (e.g., assist alongwith stamp 10 motion) selected components 23 to detach from distal ends18 of selected posts 15. If only the distal ends 18 of selected posts 15are heated by light 32, then expansion of the distal ends 18 can cause(e.g., assist along with stamp 10 motion) selected components 23 todetach from distal ends 18.

Destination substrate 70 can be any suitable substrate to whichcomponents 22 can be transferred (e.g., micro-transfer printed), forexample glass, plastic, ceramic, sapphire, semiconductor, or quartz.Substrates found in the display industry are suitable and can becommercially obtained. Destination substrate 70 can have a layer 72 ofadhesive provided on a surface of a substrate material, for example anepoxy, resin, adhesive, or polymer layer provided on a glass or plasticsubstrate material, for example SU-8. Adhesive layer 72 can assist inadhering components 22 transferred to destination substrate 70 and canbe selected to facilitate adhesion given the material qualities andsurface energies of components 22 and stamp 10. Adhesive layer 72 can bepatterned (e.g., disposed only in desired locations corresponding todesired locations for components 22).

Exemplary micro-transfer printing methods for transferring activecomponents 22 from one substrate to another are described in U.S. Pat.No. 8,889,485, entitled Methods of Surface Attachment of Flipped ActiveComponents, issued Nov. 18, 2014. Micro-transfer printing processessuitable for disposing components 22 onto destination substrates 70 aredescribed in Inorganic light-emitting diode displays usingmicro-transfer printing (Journal of the Society for Information Display,2017, DOI #10.1002/jsid.610, 1071-0922/17/2510-0610, pages 589-609),U.S. Pat. No. 8,722,458 entitled Optical Systems Fabricated byPrinting-Based Assembly, U.S. patent application Ser. No. 15/461,703entitled Pressure Activated Electrical Interconnection by Micro-TransferPrinting, U.S. patent application Ser. No. 14/822,864 entitled Chipletswith Connection Posts, U.S. patent application Ser. No. 14/743,788entitled Micro-Assembled LED Displays and Lighting Elements, and U.S.patent application Ser. No. 15/373,865, entitled Micro-TransferPrintable LED Component, the disclosure of each of which is incorporatedherein by reference in its entirety.

According to various embodiments of the present invention, componentsource wafer 20 can be provided with components 22, release layer, andtethers already formed, or they can be constructed as part of a methodin accordance with certain embodiments of the present invention.Component source wafer 20 and micro-transfer printable components 22,stamp 10, and destination substrate 70 can be made separately and atdifferent times or in different temporal orders or locations andprovided in various process states.

Methods disclosed herein can be iteratively applied to a single ormultiple destination substrates 70. By repeatedly transferringsub-arrays of micro-transfer printable components 22 from a componentsource wafer 20 to a destination substrate 70 with a stamp 10 andrelatively moving stamp 10 and destination substrate 70 between stampingoperations by a distance equal to the spacing of selected micro-transferprintable components 22 in the transferred sub-array between eachtransfer of micro-transfer printable components 22, an array ofmicro-transfer printable components 22 formed at a high density on acomponent source wafer 20 can be transferred to a destination substrate70 at a much lower density. In practice, component source wafer 20 islikely to be expensive, and forming micro-transfer printable components22 with a high density on component source wafer 20 will reduce the costof micro-transfer printable components 22, especially as compared toforming circuits on destination substrate 70. Transferringmicro-transfer printable components 22 to a lower-density destinationsubstrate 70 can be used, for example, if micro-transfer printablecomponents 22 include components 22 that manage elements (e.g., arecontrollers) distributed over destination substrate 70, for example in adisplay, digital radiographic plate, or photovoltaic system. Moreover,in some embodiments, not every post 14 of a stamp 10 is contacted to acomponent 22 during a transfer printing operation.

In some embodiments, a component 22 is an active micro-transferprintable device that is an integrated circuit formed in a crystallinesemiconductor material. The integrated circuit can comprise a substratethat provides sufficient cohesion, strength, and flexibility such thatit can adhere to destination substrate 70 without breaking as transferstamp 10 is removed.

In comparison to thin-film manufacturing methods, using denselypopulated component source wafers 20 and transferring functionalmicro-transfer printable components 22 to a destination substrate 70that requires only a sparse array of micro-transfer printable components22 located thereon does not waste or require active layer material on adestination substrate 70. Components 22 can be made with crystallinesemiconductor materials that have higher performance than thin-filmactive circuits. Furthermore, the flatness, smoothness, chemicalstability, and heat stability requirements for a destination substrate70 used in some embodiments of the present invention may be reducedbecause the adhesion and transfer process is not substantially limitedby the material properties of destination substrate 70. Manufacturingand material costs may be reduced because of high utilization rates ofmore expensive materials (e.g., component source wafer 20) and reducedmaterial and processing requirements for destination substrate 70.

Certain embodiments of the present invention provide micro-transferprinted substrates populated with only known-good components 22 withimproved yields and reduced manufacturing costs. For example,destination substrate 70 can be a display substrate and components 22can be inorganic light-emitting diodes (LEDs) in a display made at leastpartly by micro-transfer printing. Ablation layer 50, when and wherepresent, facilitates detaching selected components 23 from distal ends18 of posts 14 of stamp 10; a substantially transparent ablation layer50 enables light emitted from the inorganic light-emitting diodes topass through the ablation layer 50, enabling a display that emits lightin a direction away from the display substrate.

As is understood by those skilled in the art, the terms “over” and“under” are relative terms and can be interchanged in reference todifferent orientations of the layers, elements, and substrates includedin the present invention. For example, a first layer on a second layer,in some implementations means a first layer directly on and in contactwith a second layer. In other implementations a first layer on a secondlayer includes a first layer and a second layer with another layertherebetween.

Throughout the description, where apparatus and systems are described ashaving, including, or comprising specific components, or where processesand methods are described as having, including, or comprising specificsteps, it is contemplated that, additionally, there are apparatus, andsystems of the disclosed technology that consist essentially of, orconsist of, the recited components, and that there are processes andmethods according to the disclosed technology that consist essentiallyof, or consist of, the recited processing steps.

It should be understood that the order of steps or order for performingcertain action is immaterial so long as the disclosed technology remainsoperable. Moreover, two or more steps or actions in some circumstancescan be conducted simultaneously.

Having described certain implementations of micro-transfer printingsystems and methods of their use, it will now become apparent to one ofskill in the art that other implementations incorporating the conceptsof the disclosure may be used. Therefore, the disclosure should not belimited to certain implementations, but rather should be limited only bythe spirit and scope of the following claims.

PARTS LIST

-   10 stamp-   12 body-   14 post-   15 selected post-   16 non-selected post-   18 distal end of post-   20 component source wafer-   22 component-   23 selected component-   24 non-selected component-   30 light source-   32 light-   34 optics-   36 optical system-   38 optics controller-   39 memory-   40 motion platform-   50 ablation layer-   52 ablative material-   62 tether-   63 fractured tether-   64 anchor-   66 patterned sacrificial layer-   68 sacrificial portion-   70 destination substrate-   72 adhesive layer-   74 first locations-   76 second locations-   82 semiconductor structure-   83 component contact pads-   84 electrode-   87 patterned dielectric layer-   88 encapsulation layer/second dielectric layer-   90 test fixture-   99 micro-transfer printing system-   100 provide source wafer step-   110 provide stamp with posts step-   120 provide light source step-   130 provide destination substrate step-   140 test components to determine selected non-functional components    step-   141 test components to determine selected functional components step-   150 contact stamp posts to component step-   155 optional remove stamp from source wafer step-   160 irradiate selected posts and detach selected components step-   170 optional examine selected posts for selected components step-   180 optional determine selected components remaining on selected    posts step-   190 print non-selected components to destination substrate step-   191 move components to destination substrate step-   195 select component subset step-   200 remove stamp from destination substrate with no components step-   201 remove stamp from destination substrate with non-selected    components step-   205 move stamp with respect to destination substrate step-   210 clean stamp step-   220 determine missing component test step-   230 done step

What is claimed:
 1. A method of micro-transfer printing, comprising: providing a component source wafer having micro-transfer printable components disposed on or in the component source wafer, wherein selected ones of the micro-transfer printable components are selected components and the micro-transfer printable components that are not selected are non-selected components; providing a stamp comprising a body and spaced-apart posts protruding away from the body, the posts having a spatial distribution on the body matched to a spatial distribution of the micro-transfer printable components on or in the component source wafer; providing a light source; contacting each of the posts to a component of the micro-transfer printable components to adhere the component to the post, wherein posts contacting the selected components are selected posts and posts contacting the non-selected components are non-selected posts; removing the stamp with the adhered components from the component source wafer; and irradiating each of the selected posts through the body with light from the light source to detach the selected components adhered to the selected posts from the selected posts, leaving the non-selected components adhered to the non-selected posts, wherein the body and the posts are substantially transparent to the light.
 2. The method of claim 1, wherein the component source wafer comprises a patterned sacrificial layer defining spaced-apart sacrificial portions and anchors, and the components are each disposed over a sacrificial portion and physically connected to an anchor by a tether, and wherein the steps of contacting the posts to the components and removing the stamp fractures the tethers.
 3. The method of claim 1, comprising: providing a destination substrate; and contacting the non-selected components to the destination substrate using the stamp to adhere the non-selected components to the destination substrate or to a layer on the destination substrate after detaching the selected components from the selected posts.
 4. The method of claim 3, wherein the step of providing a destination substrate comprises providing an adhesive layer on the destination substrate and the step of contacting the non-selected components to the destination substrate comprises directly contacting the non-selected components to the adhesive layer.
 5. The method of claim 1, wherein each of the components comprises an ablation layer and wherein the irradiating the selected posts vaporizes at least a portion of the ablation layer of the selected components.
 6. The method of claim 1, wherein the selected components are disposed in contact with a destination substrate or a layer disposed on the destination substrate during the irradiating.
 7. The method of claim 1, wherein the selected components are first selected components, the non-selected components are first non-selected components, and the method comprises: providing a destination substrate; transferring the first selected components to first component locations; selecting second selected components from among the first non-selected components, wherein the non-selected posts to which the second selected components are adhered are second selected posts; and transferring the second selected components to second component locations by irradiating the second selected posts through the body with the light to detach the second selected components adhered to the second selected posts from the second selected posts.
 8. The method of claim 7, wherein the components define an array, the first selected components are a first sparse subset of the array, and the second selected components are a second sparse subset of the array.
 9. The method of claim 1, comprising testing each of the components before contacting the posts to the components to determine faulty components and selecting components that are faulty so that each of the selected components is a faulty component.
 10. The method of claim 1, comprising testing each of the components before contacting the posts to the components to determine faulty components to select components that are not faulty so that each of the selected components is a non-faulty component.
 11. The method of claim 1, comprising providing a disposal area and moving the stamp to the disposal area before the irradiating of the selected posts so that the irradiating of the selected posts detaches the selected components from the selected posts and disposes the selected components in the disposal area.
 12. The method of claim 1, comprising providing a destination substrate and moving the stamp to the destination substrate before irradiating the selected posts so that the irradiating of the selected posts detaches the selected components from the selected posts and adheres the selected components to the destination substrate or to a layer on the destination substrate.
 13. The method of claim 1, wherein the selected components are disposed over, but not in contact with, the destination substrate or the layer on the destination substrate during the irradiating.
 14. The method of claim 1, wherein the irradiating of the selected posts comprises irradiating a single post at a time.
 15. The method of claim 1, wherein the irradiating of the selected posts comprises irradiating multiple posts at a time.
 16. The method of claim 1, wherein each of the posts has a distal end away from the body and the step of contacting each post to a component comprises contacting the distal end of the post to the component to adhere the component to the distal end of the post, and wherein the irradiating of the selected posts with the light source irradiates the distal end of each selected post to detach the selected component adhered to the selected post from the distal end of the selected post.
 17. The method of claim 1, comprising providing a mapping of the selected components and the non-selected components.
 18. The method of claim 1, wherein the selected components have at least one characteristic different from a characteristic of the non-selected components.
 19. The method of claim 1, wherein the body and the posts are made from a same material.
 20. The method of claim 19, wherein the same material is polydimethylsiloxane (PDMS). 